We don't use Report Services with SQL Server, but the Report Viewer control to render reports from Azure table Storage.
That said, I believe the rendering engine is the same in both cases - and in both cases the 08 version renders header & footer content outside of the document margins.
See this Microsoft Connect discussion on the issue, and Microsoft's good 'ol "its by design" response :)
There really is no workaround you can perform in the Reports themselves - as tricking the layout to work in Word will in turn break the layout in other formats like PDF.
So crazy idea time... since a .docx file is really just a .zip fie containing a bunch of xml settings, I thought I could write a function that could modify the header & footer attributes within the file.
Lo and behold it worked really well. It works for us since we just use the Report Viewer control, and not the full-fledged Reporting Services - as we are manually working with document streams etc.
Below is a code snippet of the function. Note that it requires SharpZipLib for the zip handling. We are still on .NET 4.0 but if you are on 4.5 you could swap this out with the new ZipArchive class in the .NET framework.